GCN Circular 18337

L. P. Singer (NASA/GSFC), M. M. Kasliwal (Caltech), S. B. Cenko
(NASA/GSFC), V. Bhalerao (IUCAA), A. Miller (Caltech), T. Barlow
(Caltech), E. Bellm (Caltech), I. Manulis (WIS), A. Singhal (IUCAA), and
J. Rana (IUCAA) report on behalf of the intermediate Palomar Transient
Factory (iPTF) collaboration:

We have performed tiled observations of LIGO/Virgo G184098 using the
Palomar 48-inch Oschin telescope (P48). We imaged 18 fields spanning 135
deg2. Based on the LIB localization, we estimate a 2.3% prior probability
that these fields contain the true location of the source. The small
containment probability is because the southern mode of the updated
("LIB") localization was too far south to be observable from Palomar,
whereas most of the northern mode rose after 12�� twilight.

Sifting through candidate variable sources using image subtraction by both
our NERSC and IPAC pipelines, and applying standard iPTF vetting
procedures, we flagged the following optical transient candidates for
further follow-up:


iPTF15cyo, at the coordinates:
  RA(J2000)  =  8h 19m 56.18s (124.984069 deg)
  Dec(J2000) = +13d 52' 42.0" (+13.878337 deg)

Our P48 photometry includes:
  -483 days: R > 20.88
    +3 days: R = 17.75 +/- 0.01

The position is consistent with the galaxy SDSS J081956.62+135241.7, whose
spectroscopic redshift of z = 0.02963 implies an absolute magnitude for
the transient of M_R = -17.8, suggestive of a supernova.


iPTF15cyq, at the coordinates:
  RA(J2000)  =  8h 10m 00.86s (122.503586 deg)
  Dec(J2000) = +18d 42' 18.1" (+18.705039 deg)

Our P48 photometry includes:
  -172 days: R > 20.90
    +3 days: R = 20.05 +/- 0.10

The position is consistent with the galaxy SDSS J081000.49+184213.1, whose
spectroscopic redshift of z = 0.063192 implies an absolute magnitude of
M_R = -17.2, also suggestive of a supernova.


iPTF15cys, at the coordinates:
  RA(J2000)  =  8h 11m 55.59s (122.981632 deg)
  Dec(J2000) = +16d 43' 10.1" (+16.719465 deg)

Our P48 photometry includes:
  -611 days: R > 19.99
    +3 days: R = 17.84 +/- 0.03

The position is consistent with the galaxy SDSS J081155.51+164313.6 with
a photometric redshift of z ~ 0.087.


iPTF15cyk, at the coordinates:
  RA(J2000)  =  7h 42m 14.87s (115.561947 deg)
  Dec(J2000) = +20d 36' 43.4" (+20.612062 deg)

Our P48 photometry includes:
  -614 days: R > 22.59
    +3 days: R = 20.28 +/- 0.12

This position is consistent with the faint object SDSS
J074215.02+203648.7, which is classified by SDSS as a galaxy. The
photometric redshift is z ~ 0.77.


iPTF15cym, at the coordinates:
  RA(J2000)  =  7h 52m 35.67s (118.148623 deg)
  Dec(J2000) = +16d 45' 59.6" (+16.766542 deg)

Our P48 photometry includes:
  -157 days: R > 20.84
    +3 days: R = 19.88 +/- 0.20

This position is consistent with the faint galaxy SDSS
J075235.81+164600.4, whose photometric redshift is z ~ 0.341.


iPTF15cyn, at the coordinates:
  RA(J2000)  =  7h 59m 14.93s (119.812227 deg)
  Dec(J2000) = +18d 12' 54.9" (+18.215261 deg)

Our P48 photometry includes:
  -232 days: R > 21.69
    +3 days: R = 20.34 +/- 0.28

The position is in the nucleus of the galaxy SDSS J075914.91+181255.1,
whose spectroscopic redshift of z = 0.06158 implies an absolute magnitude
of M_R = -16.9, also consistent with a supernova.


iPTF15cyt, at the coordinates:
  RA(J2000)  =  7h 38m 59.35s (114.747288 deg)
  Dec(J2000) = +21d 45' 43.2" (+21.761996 deg)

Our P48 photometry includes:
  -240 days: R > 20.26
    +3 days: R = 19.65 +/- 0.09

The position is in the nucleus of the galaxy SDSS J073859.32+214543.1,
whose photometric redshift is z ~ 0.077.


iPTF15cyp, at the coordinates:
  RA(J2000)  =  8h 21m 43.68s (125.432006 deg)
  Dec(J2000) = +16d 12' 42.0" (+16.211667 deg)

Our P48 photometry includes:
    +3 days: R = 19.48 +/- 0.05

Earlier limits may be unreliable due to the presence of a nearby saturated
star.

The position is in the nucleus of the galaxy SDSS J082143.68+161241.6,
whose spectroscopic redshift of z = 0.02822 implies an absolute magnitude
of M_R = -16.0.


We have obtained Keck II + DEIMOS spectra of all of the above targets.
We will report our analyses of these spectra shortly.

Times are relative to the LIGO/Virgo trigger. Magnitudes are in the Mould
R filter and in the AB system, calibrated with respect to point sources in
SDSS as described in Ofek et al. (2012, http://dx.doi.org/10.1086/664065
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 ).

The diagram https://gracedb.ligo.org/apiweb/events/G184098/files/iptf.pdf
shows the locations of our candidates and the P48 fields in relation to
the LIGO/Virgo localization.

[GCN OPS NOTE(19sep15): This Circular was originally published on 03:09 18-Sep-2015 UT.]